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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 90 |
| 4 | 585 |
| 5 | 3969 |
| 6 | 27657 |
| 7 | 196290 |
| 8 | 1411965 |
| 9 | 10261485 |
| 10 | 75183147 |
| 11 | 554480316 |
| 12 | 4111617510 |
| 13 | 30628393110 |
| 14 | 229048769790 |
| 15 | 1718666596692 |
| 16 | 12933847045701 |
| 17 | 97584913269675 |
| 18 | 737953856289675 |
| 19 | 5591915004100950 |
| 20 | 42450848142844995 |
| 21 | 322796964495941235 |
[1,3,15,90,585,3969,27657,196290,1411965,10261485, 75183147,554480316,4111617510,30628393110, 229048769790,1718666596692,12933847045701, 97584913269675,737953856289675,5591915004100950, 42450848142844995,322796964495941235] |